Light-responsive current generation by phototrophically enriched anode biofilms dominated by green sulfur bacteria

The objective of this study was to employ microbial electrochemical cells (MXCs) to selectively enrich and examine anoxygenic photosynthetic bacteria for potential anaerobic respiration capabilities using electrodes. In the process, we designed a novel enrichment strategy that manipulated the poised anode potential, light, nitrogen availability, and media supply to promote growth of phototrophic bacteria while minimizing co-enrichment of non-phototrophic anode-respiring bacteria (ARB). This approach resulted in light-responsive electricity generation from fresh- and saltwater inocula. Under anoxic conditions, current showed a negative light response, suggesting that the enriched phototrophic consortia shifted between phototrophic and anaerobic respiratory metabolism. Molecular, physical, and electrochemical analyses elucidated that anode biofilms were dominated by green sulfur bacteria, and biofilms exhibited anode respiration kinetics indicative of non-mediated electron transfer, but kinetic parameters differed from values previously reported for non-phototrophic ARB. These results invite the utilization of MXCs as microbiological tools for exploring anaerobic respiratory capabilities among anoxygenic photosynthetic bacteria.